1. Field of the Invention
The present invention relates to a method for producing cross-linked polymer particles containing hydroxyl groups that can be applied to good effect in fields such as carriers of diagnostic agents and pharmaceuticals, carriers for chromatography, viscosity-controlling agents, resin-molding materials, paint additives, cross-linking/hardening agents and additives for cosmetics.
2. Description of the Related Art
Conventionally two methods have been used for producing polymer particles containing hydroxyl groups. According to the first method, polymer particles are initially formed by suspension-polymerization of monomers containing functional groups that can be converted into hydroxyl groups in an aqueous medium, and the functional groups are then converted into hydroxyl groups. According to the second method, cross-linked polymer particles containing reactive functional groups are formed, and the hydroxyl groups are then introduced into the particles by causing a hydroxyl group-containing compound to react with the reactive functional groups and thus to be linked to the particles.
Examples known in the art of polymer particles produced by the first method include porous and spherical separation carriers obtained either by homo-polymerization of an aqueous suspension of pentaerythritol dimethacrylate, or by aqueous co-polymerization of pentaerythritol dimethacrylate with a methacrylate monomer containing hydrophilic groups and/or groups that can be converted into hydrophilic groups (for example, see Japanese Patent Application Publication (JP-B) No. 61-36177). However, since pentaerythritol dimethacrylate is not industrially manufactured on a large scale, users first need to manufacture pentaerythritol and thus the process becomes complicated.
In a variation of the first method disclosed, ester groups of a co-polymer obtained by co-polymerization of carboxylic acid vinyl ester monomers and cross-linking monomers containing isocyanulate rings are converted into hydroxyl groups by saponification (for example, see JP-B No. 2-19902). However, the hydroxyl group obtained by saponification of the carboxylic acid vinyl ester is restricted to a polyvinyl alcohol-type hydroxyl group directly linked to the main chain, and a drawback of this method is that chemical structures surrounding the hydroxyl group cannot be modified. In addition, since carboxylic acid salts cannot easily be removed from the inside of the particles after alkali-hydrolysis, the process used by following this method has also tended to become complicated.
As the second method disclosed for producing the hydrophilic separation carrier containing the hydroxyl groups, a cross-linked co-polymer of (meth)acrylic acid ester containing glycidyl groups is made to perform a ring-opening reaction with polyethyleneglycol or glycerin (Japanese Patent Application Laid-open (JP-A) No. 60-96605). However, since a reactive functional group such as the glycidyl group tends to cause side reactions, and it becomes difficult to control the amount of the hydroxyl group, the properties of the desired particles have tended to be adversely affected. Furthermore, (meth)acrylic ester containing a glycidyl group is toxic and its use is not desirable in terms of safety or hygiene.
In a variation of the second method disclosed, fine particles of a cross-linked polymer containing reactive functional groups, selected from an epoxy group (such as the glycidyl group), an hydroxyl group and a carboxylic group are made to react with a polyethyleneglycol (Japanese Patent Application Laid-Open (JP-A) No. 5-1106). However, control of the amount of the hydroxyl group and control of particle properties as the object of the method are difficult, insofar that in this production method the hydroxyl group originating from polyethyleneglycol, and the hydroxyl group and carboxylic group inherent in the particles tend to become mixed together. Moreover, use of an epoxy group (such as the glycidyl group) also entails the same problems as with the use of a glycidyl group.
Conventional production methods for obtaining hydroxyl group-containing polymer particles have thus so far entailed the problems described above.